1. Field
The following description relates to an optical lens, and more particularly, to a variable-focus liquid lens.
2. Description of the Related Art
The development of digital technologies is accelerating digital convergence. Applications of digital convergence are most active in the fields of media and communication, and a primary example of a digital convergence product is a mobile communication device. Mobile communication devices are incorporated not only with devices that offer gaming, music playback, broadcasting and Internet functions, but also with image pickup devices such as digital cameras and digital camcorders. In particular, image pickup devices are being widely installed in mobile phones and other mobile electronic devices such as laptop computers and personal digital assistants (PDAs).
Mobile electronic devices equipped with an image pickup device, which has recently gained popularity, are becoming smaller and thinner. Accordingly, image pickup devices are also required to be smaller, lighter, and cost-effective. In particular, the recent trends that a mobile communication device includes not only an image pickup device but also other digital electronic devices (e.g., an MP3 player, a video player, a digital multimedia broadcasting (DMB) television, and the like) contributes to an increase in demands for smaller and cost-effective image pickup devices. Wafer-level image pickup devices are small camera modules designed to meet the demands for smaller, thinner, and more economical image pickup devices.
In early days when mobile electronic devices containing image pickup devices were first available, the demands on the performance (e.g., resolution) of the image pickup devices were not that high. However, as the type of mobile electronic devices equipped with an image pickup device has become more and more diverse to meet the various needs and preferences of consumers, the demands on the performance of image pickup devices is also increasing. For example, image pickup devices of mobile electronic devices had offered a close-up function with a close-up distance of 60 cm, with a fixed focal length. Nowadays, image pickup devices have an auto-focus function, a zoom function, and a close-up function with a close-up distance of 30 cm or less.
To implement the auto-focus function, the zoom function, and the close-up function in image pickup devices, variation in the focal length of a lens is essential. One way of enabling wafer-level image pickup devices to have a variable focus is to use a liquid lens. A liquid lens is an optical lens having a transparent fluid which is contained in a transparent membrane. Specifically, a liquid lens is an optical lens that can change its focal length by applying a predetermined force to the fluid which is contained in a membrane, and thus changing the shape (i.e., curvature) of a surface of the membrane. Since liquid lenses can be manufactured small, they are suitable for use as variable-focus optical lenses of wafer-level image pickup devices.